The present invention relates to a brazing alloy. In particular, the present invention relates to a Ni-base brazing alloy, the alloy having a good wetting and flowing property (to be referred to as wettability), an excellent corrosion resistance and a high strength. The alloy is used for process of joining two pieces of metal such as stainless steel.
A Ni-base brazing filler metal, defined as JIS standard (Japanese Industrial Standard) of JIS Z3265 and AWS (American Welding Society) standard of ANSI/AWS A5.8, is generally used for the process of brazing stainless steel to produce various kinds of products such as a heat exchanger and a gas turbine.
Recently, it is significantly required to provide a brazing alloy having a corrosion resistance in sulfuric acid and so on, which may be brazed at a temperature as low as possible, to form a brazed joint of high strength. The Ni-base brazing filler metal as a prior art however has several objects as follows.
As Ni-base brazing filler metal defined in the JIS and the AWS standard, there is known the alloy BNi-5 having Nixe2x80x94Crxe2x80x94Si composition, which has a good corrosion resistance. However, it has a high liquidus of 1150xc2x0 C. so that it requires to be heated up to 1200xc2x0 C. for brazing, during which the property of the stainless steal would be decreased.
There are also known the alloys BNi-1, 1A and 2 having Nixe2x80x94Crxe2x80x94Fexe2x80x94Sixe2x80x94B composition and the alloys BNi-3 and 4 having Ni-Si-B composition, which provide a property of a high strength of the brazed joint, but the corrosion resistance of the stainless steel may decreased due to diffusion of B when brazed.
There are also known the alloys BNi-6 and 7 having Nixe2x80x94(Cr)xe2x80x94P composition, which may be brazed at a comparatively low temperature of about 1000xc2x0 C. These alloys also have a good wettability, but are brittle to have a low strength of the brazed joint.
On the other hand, the present inventors already disclosed Ni-base brazing alloys having a heat resistance in Japanese laid open patent application No. 9-225679 of 1997. The alloys disclosed in the above application may be brazed at a temperature as low as BNi-2. However, there found some part of the composition of the alloy defined in the application to form a slag when brazed, which may lead to have a low strength of the brazed joint.
Therefore, it is required to provide a Ni-base brazing alloy used for process of joining two pieces of metal such as stainless steel, and with the alloy brazed at a temperature as low as possible, for example at about 1100xc2x0 C., to thereby prevent the property of the stainless steel from being decreased. The alloy is also accompanied with characteristics that no slag is formed when brazed, and that it has a good wettability, a high strength of the brazed joint, and an excellent corrosion resistance in sulfuric acid and so on
In order to provide the alloy having above required characteristics, the present inventors have reviewed the prior alloy having a Nixe2x80x94Crxe2x80x94Pxe2x80x94Si composition disclosed in Japanese laid open patent publication No. 9-225679 of 1997 to find the present alloy having a noble composition with further additives.
According to the present invention, the present alloy has a noble composition relative to above identified application. Thus, the present alloy contains Cr in an increased amount to be designed to improve the strength, which keeps having a preferable melting point and corrosion resistance. While the present alloy also contains Cr, P and Si, each amount of Cr, P and Si and the total amount of P and Si are designed the alloy to have a hypo-eutectic structure. The present alloy further contains Al, Ca, Y and/or misch metal in a small amount so that the alloy is designed to prevent a slag from forming when or after brazed and to improve the wettability. The present alloy also contains Fe, Co, Mo and/or V in an amount not to negatively influence its melting point, its wettability and its corrosion resistance so that the alloy is improved to have a higher strength, in particular of the brazed joint.
Thus, there is provided a Ni-base brazing alloy comprising Cr in an amount of 25 to 35%, P in an amount of 4 to 8%, Si in an amount of 3 to 6%, with the total amount of P and Si being 9 to 11.5%, at least one element selected from a group consisting of Al, Ca, Y and misch metal in an amount of 0.01 to 0.10%, and the balance of Ni and unavoidable impurities, by weight.
If necessary, the alloy further comprises at least one element selected from a group consisting of Fe in an amount of 20% and less, Co in an amount of 20% and less, Mo in an amount of 10% and less, and V in an amount of 5% and less, with the total amount of Fe, Co, Mo and V being 20% and less, by weight.
The additional advantages and characteristic features of the present invention will become apparent to those skills in the art by the following detailed description together with the appended drawing.